1. Field of the Invention
The present invention relates to an apparatus and method for transmitting and receiving resource allocation information in a communication system.
2. Description of the Related Art
Future-generation communication systems are under development to provide various high-speed, large-capacity services to Mobile Stations (MSs). An example of a future-generation communication system includes an Institute of Electrical and Electronic Engineers (IEEE) 802.16m communication system.
With reference to FIG. 1, a method for transmitting resource allocation information in an IEEE 802.16m system will be described below.
FIG. 1 illustrates a subframe structure in an IEEE 802.16m communication system according to the related art.
Before describing FIG. 1, a description will first be given of a frame structure in the IEEE 802.16m communication system.
In the IEEE 802.16m communication system, a superframe includes a predefined number of frames, each frame having a predefined number of subframes. Each of the subframes includes a predefined number of Orthogonal Frequency Division Multiple Access (OFDMA) symbols. The numbers of DownLink (DL) frames and UpLink (UL) frames in a superframe are determined according to a predefined DL-to-UL ratio. The number of frames per superframe, the number of subframes per frame, the number of OFDMA symbols per subframe, and the ratio between DL frames and UL frames in a superframe may be changed.
Resource allocation is performed with the resources of each subframe in the IEEE 802.16m communication system. The resources of each subframe are allocated on a unit basis, for example, on a Resource Block (RB) basis. Upon completion of an allocation of the resources of a subframe, resource allocation information specifying the allocated resources is transmitted in the subframe. The allocated resources include at least one RB and the resource allocation information is delivered in, for example, a MAP message, which will be described with reference to FIG. 1.
Referring to FIG. 1, it is assumed that one DL subframe is allocated to, for example, four MSs, MS #1 to MS #4. For convenience in description, resources allocated to MS #1 are referred to as MS #1 resources, resources allocated to MS #2 are referred to as MS #2 resources, resources allocated to MS #3 are referred to as MS #3 resources, and resources allocated to MS #4 are referred to as MS #4 resources. Resource allocation information about the MS #1 resources is transmitted in an MS #1 MAP message, resource allocation information about the MS #2 resources is transmitted in an MS #2 MAP message, resource allocation information about the MS #3 resources is transmitted in an MS #3 MAP message, and resource allocation information about the MS #4 resources is transmitted in an MS #4 MAP message. The MS #1 MAP message is a MAP message carrying the resource allocation information about the MS #1 resources, the MS #2 MAP message is a MAP message carrying the resource allocation information about the MS #2 resources, the MS #3 MAP message is a MAP message carrying the resource allocation information about the MS #3 resources, and the MS #4 MAP message is a MAP message carrying the resource allocation information about the MS #4 resources.
To allocate resources as described above, MAP messages are used for resources in a one-to-one correspondence and should carry resource allocation information about the resources. Accordingly, the overhead of transmitting resource allocation information increases with the number of allocated resources, thereby decreasing the overall system performance of the IEEE 802.16m communication system.
Resource allocation can be considered in two ways, individual resource allocation and group resource allocation in the IEEE 802.16m communication system. Depending on individual or group resource allocation, resource allocation information may be represented differently.
In the case of individual resource allocation, four schemes are available to represent resource allocation information, namely a start-end scheme, a start-length scheme, a tree scheme, and a triangle scheme.
The start-end and start-length schemes will first be described below with reference to FIG. 2.
FIG. 2 illustrates start-end and start-length schemes used to represent resource allocation information in an IEEE 802.16m communication system according to the related art.
Referring to FIG. 2, it is assumed that one subframe includes, for example, 48 RBs, RB #0 to RB #47. The start-end scheme specifies resource allocation information using a start position index indicating the start position of allocated resources and an end position index indicating the end position of the allocated resources. For example, if the allocated resources include 9 RBs, RB #20 to RB #28, resource allocation information about the allocated resources is specified using a start position index ‘000000010100’ and a last position index ‘000000011100’. Given 48 RBs for a subframe, resource allocation information about allocated resources of the subframe may be represented in 24 bits.
The number of bits used to represent resource allocation information about allocated resources in the start-end scheme may be determined by the following equation,Bit Overhead for Start-End Scheme=2┌ log2(NRB)┐(Bits)  (1)where Bit overhead for Start-End Scheme denotes the number of bits used to represent resource allocation information in the start-end scheme and NRB denotes the number of RBs included in a subframe.
The start-length scheme specifies resource allocation information using a start position index indicating the start position of allocated resources and a length index indicating the length of the allocated resources. For example, if the allocated resources include 9 RBs, RB #20 to RB #28, resource allocation information about the allocated resources is specified using a start position index ‘000000010100’ and a length index ‘000000001001’. Given 48 RBs for a subframe, resource allocation information about allocated resources of the subframe may be represented in 24 bits.
The number of bits used to represent resource allocation information about allocated resources in the start-length scheme may be determined by the following equation,Bit Overhead for Start-Length Scheme=2┌ log2(NRB)┐(Bits)  (2)where Bit Overhead for Start-Length Scheme denotes the number of bits used to represent resource allocation information in the start-length scheme.
With reference to FIG. 3, the tree scheme will be described below.
FIG. 3 illustrates a tree scheme in an IEEE 802.16m communication system according to the related art.
Referring to FIG. 3, it is assumed that a subframe includes, for example, 48 RBs, RB #0 to RB #47. According to the tree scheme, resource allocation information may be represented by node indexes. While the tree scheme reduces bit overhead relative to the start-end scheme and the start-length scheme, it has a decreased freedom of representing resource allocation information. More specifically, resource allocation information can be represented only for resources having a size of a power of 2 and a start position being a multiple of 2 in the tree scheme. For instance, if allocated resources occupy 8 RBs ranging from RB #0 to RB #7, the allocated resources may be indicated by resource allocation information. However, if allocated resources occupy 8 RBs ranging from RB #1 to RB #8, the allocated resources may not be indicated by resource allocation information. Despite the advantage of reduction of bit overhead, therefore, the tree scheme faces a limited resource allocation freedom.
The number of bits used to represent resource allocation information about allocated resources in the tree scheme may be determined by the following equation,Bit Overhead for Tree Scheme=┌ log2(NRB)┐+1(Bits)  (3)where Bit Overhead for Tree Scheme denotes the number of bits used to represent resource allocation information in the tree scheme.
With reference to FIG. 4, the triangle scheme will be described below.
FIG. 4 illustrates a triangle scheme in an IEEE 802.16m communication system according to the related art.
Referring to FIG. 4, it is assumed that a subframe includes, for example, 48 RBs, RB #0 to RB #47. The triangle scheme increases the resource allocation freedom by increasing the number of nodes, relative to the tree scheme. Therefore, the triangle scheme has a higher bit overhead than the tree scheme. In FIG. 4, since one subframe includes 48 RBs, the triangle scheme should be able to express a total of 1176 cases. Hence, 11 bits are used to represent resource allocation information. The number of bits used to represent resource allocation information about allocated resources in the triangle scheme may be determined by the following equation,Bit Overhead for Triangle Scheme=┌ log2(NRB(NRB+1)/2)┐(Bits)  (4)where Bit Overhead for Triangle Scheme denotes the number of bits used to represent resource allocation information in the triangle scheme.
In the case of group resource allocation, resource allocation information may be represented using a bitmap scheme. The bitmap scheme will be described below with reference to FIG. 5.
FIG. 5 illustrates a bitmap scheme in an IEEE 802.16m communication system according to the related art.
Referring to FIG. 5, it is assumed that a subframe includes, for example, 48 RBs, RB #0 to RB #47. Allocated RBs and non-allocated RBs are indicated in a bitmap. The RBs of the subframe are mapped to bits in a one-to-one correspondence. If an RB is allocated, a bit mapped to the RB is set to, for example, ‘1’. If the RB is not allocated, the bit mapped to the RB is set to, for example, ‘0’. If one subframe includes 48 RBs as illustrated in FIG. 5, the bitmap scheme uses 48 bits.
The bitmap scheme may indicate whether a specific RB is allocated or not, but may not distinguish between allocated resources. This means that it is not possible to identify the start and end of allocated resources from a bitmap. Accordingly, the bitmap should be transmitted along with information about the positions of allocated resources and information for distinguishing the allocated resources from other resources in the bitmap scheme, thereby increasing bit overhead.
As described above, the methods for representing resource allocation information in the case of individual resource allocation, that is, the start-end scheme, the start-length scheme, the tree scheme, and the triangle scheme increase bit overhead linearly as the number of allocated resources increases. As a consequence, the overall system performance of the IEEE 802.16m communication system is decreased.
In the case of group resource allocation, resource allocation information may be represented in the form of a bitmap. This bitmap scheme does not increase bit overhead with the number of allocated resources but requires additional transmission of information about the positions of allocated resources and information for distinguishing the allocated resources from other resources, thereby eventually increasing bit overhead and thus decreasing the overall system performance of the IEEE 802.16m communication system.